A retinal imaging Adaptive Optical(AO) system with a large Field of View(FOV) was designed to expand the FOV of the retinal image of liquid crystal AO system. Based on analysis of the AO retinal imaging system under an isoplanatic angle, it pointed out that the FOV for wave-front detection should be smaller than a half isoplanatic angle for precise wave-front detection and the half FOV should not be larger than the isoplanatic angle in imaging. A coaxial wave-front detection and optical imaging system was fabricated, meanwhile, an adjustable pupil was used to switch the different FOVs for wave-front detection and imaging, respectively. After adaptive optical wave front correction, the wave-front error is significantly reduced and the FOV for imaging is enlarged from a diameter of 200 μm to 500 μm without any harmful effect on imaging quality. By utilizing an adjustable pupil in the system based on the isoplanatic angle, the retinal image FOV has increased by 2.5 times as compared with that of existing AO system. The applicability of the system on clinical practice is increased a lot by this research.